Asymmetric pneumatic tires



Nov. 18, 1969 H. MIRTAIN ET AL ASYMMETRIC PNEUMATIC TIRES Original FiledMay 18, 1966 2 Sheets-Sheet 1 INVENTOR3 HEM?! I P714 721 y Awe: Owls/W6W IMZ.

Arm/FIVE) NOV. 18, 1969 MIRTAIN ETAL Re. 26,713

ASYMMETRIC PNEUMATIC TIRES Original Filed May 18. 1966 2 Sheets-Sheet zBY fl/vapc' DEV/51m:

United States Patent Int. Cl. B60c 9/02, 13/00 US. Cl. 152353 ClaimsMatter enclosed in heavy brackets II] appears in the original patent butforms no part of this reissue specification; matter printed in italicsindicates the additions made by reissue.

ABSTRACT OF THE DISCLOSURE In a standard belted radial ply pneumatictire in service on a vehicle, an uncontrolled lateral slip force may begenerated, the components of which are a laterally d rected force ofstructure resulting from the interaction of the cords of the outermostbreaker ply with the road, the direction of this force depending on thedirection of rotation of the tire but not on its direction of mounting,and a laterally directed force of conicity resulting from the geometryof the tire, the direction of this force depending on the direction ofmounting of the tire but not its direction of rotation. T 0 provide fora controlled lateral slip force, a predetermined geometrical asymmetryis deliberately incorporated in the tire, and concurrently the manner ofmounting of the tire on a vehicle is accurately specified, to ensurethat when the vehicle is moving forwardly, the force of conicity isdirected vectorially opposite to the force of structure.

This invention relates to pneumatic tires for vehicles, and moreparticularly to the type of tires generally called radial or radial plytires.

The expressions radial tires and radial ply tires" as commonly used inthe pneumatic tire art may be said to include various tire constructionshaving one or more reinforcement plies of weftless cord fabric extendingfrom bead to bead wherein the cords in each ply are substantially radialin orientation, i.e. the cords are oriented substantially normal to thebeads and the crown centerline of the tire. In a monoply radial tireconstruction, the cords normally have a 90 bias angle, i.e. in theunshaped carcass they extend perpendicular to the planes of the beads.In a two-ply radial tire construction, the cords in each body ply areusually oriented at oppositely disposed small angles of up to 10 withrespect to the perpendicular to the bead planes, in which case therespective body plies are said to have oppositely disposed bias anglesof 80 or greater (but less than 90). In four-ply or heavier radial tireconstructions, similar opposed orientation of the cords in successivebody plies is usually employed. All of these body or carcassconstructions are contemplated within the scope and meaning of theexpressions "radial and substantially radia as used herein.

The present invention stems from the recognition of the fact that tiresare not always rigorously uniform. That is to say, tires are found tohave both radial and lateral variations in uniformity. Even withouttaking into account the radial and lateral eccentricity resulting fromgenerally accepted tolerances in the wheel rims on which tires aremounted, therefore, these variations in the uni- Re. 26,713 ReisswedNov. 18, 1969 formity of the tire cause the tire and rim combinationviewed as a whole to have variations of radial and lateral forces. Thisapplies even in the case of radial ply tires in which a breaker or beltis incorporated in the tire between the crown region of the carcass andthe surrounding tread band.

We have now discovered that apart from the abovementioned variations inuniformity resulting from the structure and manufacture of the tire, aneffective lateral force on the tire may also exist due to the reactionbetween the tire and the ground. This force, which will hereinafter bereferred to as the lateral slip force, generally has two components, (a)a force due to the structure of the tire itself, hereinafter designatedby the term force of structure and symbol F, and (b) a force resultingfrom the geometry of the tire, hereinafter designated by the term forceof conicity" and symbol C.

The force of structure F, for a given direction of rotation of the tire,is always directed in the same lateral direction relative to its medianequatorial plane [for any given tire] irrespective of the direction ofmounting of the tire [thereof] on the wheel rim, by virtue of [and itsdirection results from] the orientation of the generally inextcnsiblemetal wires constituting the cord elements of the outermost reinforcingply of the breaker or belt placed under the tread. The lateral force ofconicity C in a standard radial tire, however, for the given directionof rotation thereof may be [usually is] directed sometimes in onedirection and sometimes in another, depending on the direction ofmounting [rotation] of the tire.

The total lateral force L thus is given by the equation from which itwill be seen that if for a given (say, the positive) direction ofrotation of the tire, achieved by a forward movement of the vehicle,both the force of structure F and the force of concity C are positive,the total lateral force is Thus, the effects of the two forces areadded. In the reverse (i.e. the negative) direction of rotation of thissame tire, achieved by a forward vehicle movement with the direction ofmounting of the tire reversed. the force of structure F is stillpositive, but the force of conicity C is now negative, whereby theresultant, i.e. the total lateral force, is expressed by the relation Lthus is lower when the tire rotates in the second case [negativedirection] than when it rotates in the first case [positive direction].

We have further discovered that the total lateral slip force L is animportant factor in the cornering ability of the vehicle on which suchtires are mounted. Thus, for example, if at the front of such a vehiclethe sum of the lateral forces of the two tires, which sum may be as highas 2L, exceeds a certain value, the vehicle tends to pull to the rightor to the left depending on the direction of L, i.e. the vehicle tendsto over-steer or under-steer.

It is an object of the present invention, therefore, to provide meansenabling such potential disadvantage to be avoided.

A more specific object of the present invention is the provision ofnovel constructions of radial ply tires, as well as novel methods ofmanufacturing such tires, by means of which the force of structure F ofeach tire is eflectively counteracted [counterbalanced] at all times bythe force of conicity C of the same tire.

Generally speaking, these objectives of the invention are achieved bybuilding the tire in such a way that with the force of structure F forforward or normal driving movement of the vehicle always directed in asingle lateral direction, i.e. positive or negative, regardless of theactual direction of mounting of the tire on the wheel rim, the force ofconicity is always vectorially opposite to the force F for the same[regardless of the] direction of movement [rotation] of the vehicle[wheel]. The sufficient condition is then expressed by the relationalthough it would be preferred if the magnitude of C were greater thanthe magnitude of F.

In accordance with our invention, this objective is basically attainedby the provision of means in the tire, constituting a part of thestructure thereof, establishing [of] an asymmetry of the geometry of thetire which, with reference to the median equatorial plane of the tire,is sufficient to cause the difference in the resistance of therespective sidewalls to deflection in service, in combination with meansfor indicating the manner in which the tire should be mounted to achievethe desired opposition of the forces of structure and conicity duringnormal forward driving movement of the vehicle.

We are, of course, aware of the fact that asymmetrical tireconstructions have heretofore been proposed for various reasons. Webelieve, however, that all such known constructions have been devisedwithout any consideration of the relationship between the force ofconicity C and [to affect, and are capable of affecting, only] the forceof structure F, [particularly to the end of increasing that force,] andin particular have not in any way been devised to create a deliberatelychosen [vectorially opposite] force of conicity C vectorially oppositeto the force of structure F through the creation of a predetermineddiffererence between the deflection characteristics of the two sidewallsof a tire.

Basically, a tire according to the present invention, which includes aradial ply carcass, a tread, a breaker forming the reinforcement for thetread, and two sidewalls, is characterized by the fact that theeffectiveness of the reinforcement means in one sidewall differs fromthe reinforcement means in the other sidewall.

In accordance with one aspect of the present invention, therefore, thetire is molded asymmetrically with respect to its equatorial plane, thecurvature of one sidewall being greater than that of the other.According to another aspect of the present invention, the sidewalls arecomposed of respective rubber stocks of different moduli. According to athird aspect of the present invention, the thickness of one sidewall isdifferent from the thickness of the other. According to a fourth aspectof the present invention, the carcass reinforcing the sidewalls isconstituted at least in part by two ply sections either interrupted orjoined under the breaker, each ply section being composed of a cordmaterial the elongation characteristics of which differ from those ofthe cord material used in the other ply section. According to a fifthaspect of the present invention, the number of reinforcement plies inone sidewall is different from that in the other sidewall. In all ofthese variants, the tire is provided with means indicating the requiredmanner of mounting thereof for the purpose aforesaid.

The foregoing and other objects, characteristics and advantages of thepresent invention will be more clearly understood from the followingdetailed description thereof when read in conjunction with theaccompanying drawings, in which:

FIG. 1 is a diagrammatic transverse or radial section through anillustrative type of tire provided with an asymmetrical structureaccording to the basic principles of the present invention;

FIG. 2, 3 and 4 are similar views of other types of tires embodying avariant of the present invention and illustrate the tires before andafter a post-cur treatment through which the desired asymmetry isachieved; and

FIG. 4A is a similar view of the type of tire shown in FIGS. 3 and 4 buthaving an asymmetry which is a somewhat modified version of that shownin FIG. 4.

Referring now to the drawings in greater detail, FIG. 1 illustrates aradial ply tire 10 comprising a carcass 11, sidewalls 12 and 13terminating at their radially inwardmost ends in beads 14 and 15,respectively, a tread 16 surrounding the crown portion of the carcass,and a breaker or belt 17 interposed between the carcass and the tread toreinforce the latter. The carcass 11 is composed of one or more plies ofrubberized tire fabric 18 in each of which the cord elements (ofmetallic wires, or of filaments of nylon, polyester, glass, etc.) extendat an angle of between about and to the median equatorial plane X-x ofthe tire.

As is well known, the breaker 17 may be either a single ply or amulti-ply structure, composed of usually weftless rubberized cord fabricin which the generally inextensible cord elements are made either ofmetallic wires or of suitable synthetic non-metallic filaments of glass,nylon, polyester, and the like. Such cord elements are orientedgenerally circumferentially of the tire and are said to have a low biasangle (the angle between their direction of orientation and the medianequatorial plane xx of the tire). For truly circumferential breakercords, the bias angle thus is zero, but in practice the breaker cordsare usually oriented at a small angle to the median equatorial plane x-xof the tire (in a multiply breaker the cords in successive plies areoriented at opposite low bias angles). As previously indicated, it isprincipally the bias angle of the radially outermost breaker ply whichimparts to the tire its force of structure F, and in FIG. 1 this forceis assumed to be directed as shown by the relatively long clear arrowtoward the sidewall 13 which, designated by a relatively short cleararrow I, is to be the inner sidewall of the tire 10 when the latter isin use, i.e. the sidewall which will face inwardly of the vehicle onwhich the tire is mounted.

In accordance with one aspect of the present invention, to achieve theobjective of imparting to the tire 10 the eccentricity or asymmetryneeded to ensure the creation of the force of conicity C vectoriallyopposed, as indicated by the dark arrow in FIG. 1, to the force ofstructure F, the outer sidewall 12, designated by the short clear arrowE, is provided with a greater curvature than the inner sidewall 13. Thisis graphically represented in FIG. 1 by the difference between thedimensions a and b. By virtue of such a construction, it will be readilyunderstood, the outer sidewall of the tire will have a lower resistanceto deflection under load than the inner sidewall, which is manifestedunder load by a slight inclination of the tread 16 toward the outside ofthe vehicle, i.e. so that the plane of contact between the surface ofthe tread and the road is not truly perpendicular to the median planex--x of the tire. Similar results, albeit to a lesser degree, may beachieved, in accordance with other aspects of the present invention, byutilizing rubber stocks of appropriately different moduli in themanufacture of the sidewalls 12 and 13, or by making the sidewalls ofappropriately different thicknesses.

Nevertheless, we have found that the objectives of our invention can beattained more readily and to greater advantage through the use of aconstitutive asymmetry of the carcass of the tire, e.g. by making thereinforcement for the outer sidewall less stretchable than thereinforcement for the inner sidewall. Thus, the tire 10a shown in FIG. 2(parts of which identical to those of the tire 10 in FIG. 1 aredesignated by the same reference numerals) comprises a radial plycarcass 119. which is constructed of an inner ply 18 having cordelements made of nylon filaments, for example, and an outer ply definedby separate ply sections 19 and 20 of cord fabric joined to each otheralong the median plane x-x under the breaker 17, the cord elements inthe section 19 at the outer sidewall 12 being made of rayon filaments R,and the cord elements in the section 20 at the inner sidewall 13 beingmade of nylon filaments N. On the other hand, the tire b shown in FIG. 3comprises a radial ply carcass which is interrupted under the breaker17, i.e. constructed of separate ply sections 21 and 22 at the outer andinner sidewalls, respectively, and made of rayon and nylon tire cords,respectively.

It should be understood, of course, that other cord materialcombinations for the plies 19-20 and 21-22 are also possible, subjectonly to the requirement that the cord material used for the ply section19 or 21 to be incorporated in the outer sidewall 12 be less stretchablethan the cord material used for the ply section or 22 to be incorporatedin the inner sidewall 13. It will also be apparent that alternativelythe requisite differential in stretchability can be achieved even whenonly one type of cord material, e.g. nylon, is used throughout thecarcass, or when the cord material in the outer sidewall ply section ismore stretchable than the cord material in the inner sidewall plysection, by incorporating a suitably greater number of ply sections (notshown) in the outer sidewall than in the inner sidewall.

As will be clear to those skilled in the art, therefore, when such atire is being shaped and cured, the tread and breaker region thereof isby and large symmetrical with respect to the median equatorial plane xxof the tire. This condition is indicated in FIGS. 2 and 3 by the dotdashlines yy extending through the respective pairs of shoulders of thetires 10a and 10b at right angles to the planes x-x. Thereafter, at theend of the curing cycle, the tire is removed from the press or mold andis immediately post-inflated while still hot. The inner sidewallstructure of the tire will thus be stretched somewhat more than theouter sidewall structure, e.g. due to the use of nylon cords N in theformer and rayon cords R in the latter, whereby the tread and breakerregion assumes a somewhat conical shape in cross-section, shown in FIG.4, for the sake of simplicity, only for the tire 10b. This condition isindicated in FIG. 4 by the dot'dash line y'--y' extending through theshoulders of the tire at a small angle a to the line yy which is stillshown as perpendicular to the plane x--x. Accordingly, since the radiusof the tread and breaker region, as measured from the axis of rotationof the tire, is less at the outer sidewall than at the inner sidewall,the resulting eccentricity or asymmetry of the tire ensures that thelatter, when in use, will be subjected to a lateral force C, i.e. theforce of conicity, directed oppositely to the force of structure F andof sufiicient magnitude effectively to counteract [counterbalance] thesame.

FIG. 4A shows a possible variant of the foregoing, in which the tire 10cdiffers from the tire 10b only in that the outer sidewall 12a is madesomewhat thicker than the inner sidewall 13 to help accentuate thedifference in the stretchability or the resistance to deflectionthereof, it being understood that such a difference in sidewallthickness may be applied as well to tires of the type designated 10a inFIG. 2, to tires using different numbers of carcass plies (whether ofthe same or different cord materials) in the respective sidewalls, andto tires using rubber stocks of different moduli in the respectivesidewalls.

By means of the present invention, therefore, we are able to producetires each having a supplied and predeterminable geometrical asymmetrythe operational result of which is a force of conicity sufficienteffectively to counteract [counterbalance] the inherent and invariableforce of structure of the tire. The term invariable is here used only todenote the fact that in any tire manufacturing run all tires of asequential set will generally utilize the same breaker fabric andconstruction, and will have the breaker applied in essentially the sameway; quite obviously, differences in tire building techniques, such aschanges in or even reversals of the bias angle of the cords in theoutermost breaker ply, etc. may yield different magnitudes and vectorialdirections of the force of structure F. Since each tire according to ourinvention will be clearly marked to designate which sidewall is theinner and which the outer, each set of tires on a given vehicle may thenbe so mounted that the paired and generally oppositely directedresultants L of the forces F and C will cancel each other, therebyproviding a more stable handling of the vehicle, especially duringcornering, by virtue of the substantial minimization of the tendency ofthe set of tires to exert a lateral drag on the vehicle. Moreover, ourinvention is of substantial importance to the tire manufacturer from thestandpoint of economies, since the imposition of a deliberately choseneccentricity or asymmetry on each tire produced will appreciably reducethe number of tires in any given manufacturing run which will have to berejected as unfit for actual use due to the fact that more tires can bematched up for paired use on a vehicle.

It is to be understood that the foregoing description is illustrativeonly, and that the various tire constructions disclosed herein aresusceptible to a number of variations and modifications none of whichinvolves a departure from the spirit and scope of the present inventionas defined in the hereto appended claims.

Having thus described our invention, what we claim and desire to secureby Letters Patent is:

l. A pneumatic tire, comprising a carcass constituted by at least oneply of substantially radially oriented tire cords, sidewalls reinforcedby said carcass, a tread surrounding the crown region of said carcass, abreaker interposed between said carcass and said tread, said breakerbeing substantially coextensive with said crown region and comprised atits radially outermost region of generally inextensible tire cordsoriented at a small angle to the median equatorial plane of the tire,thereby to impart to the latter when in service on a moving vehicle alateral force of structure the direction of which, with reference tosaid plane, is dependent on the direction of rotation [directed at alltimes toward the same one of the sidewalls] of the tire but independent[irrespective] of the direction of mounting of the latter on the wheelrim, [and] means constituting a part of the structure of the tire toestablish in the same an asymmetry of its geometry thereby to impart tothe tire when in service on a moving vehicle a lateral force of conicitythe direction of which, with reference to said plane, is dependent onthe direction of mounting of the tire on the wheel rim but independent[directed at all times opposite to said force of structure irrespective]of the direction of rotation of the tire, and means associated with thetire for indicating the manner in which the tire should be mounted foruse on a vehicle so as to ensure that upon forward movement of thevehicle the direction of said force of conicity of the tire is in asense vectorially opposite to that of its [having a magnitude sufficientefiectively to counterbalance said] force of structure.

2. A tire according to claim 1, said first-named means comprising theprovision of sidewalls having different curvatures.

3. A tire according to claim 1, said first-named means comprising theprovision of sidewalls having different thicknesses.

4. A tire according to claim 1, said first-named means comprising theprovision of sidewalls made of rubber stocks having different moduli.

5. A tire according to claim 1, said first-named means comprising theprovision of sidewalls reinforced by different numbers of carcass plies.

6. A tire according to claim 1, said first-named means comprising theprovision of sidewalls reinforced by respective carcass ply sections thecord elements of which are made of materials having differentstretchability characteristics.

7. A tire according to claim 6, wherein the cord elements in one of saidply sections are made of rayon and in the other of said ply sections ofnylon.

8. A tire according to claim 6, wherein said ply sections are unitedwith each other under said breaker.

9. A tire according to claim 6, wherein said ply sections areinterrupted under said breaker.

10. A tire according to claim 6, wherein said cord elements arestretched different amounts to impart to the tire an asymmetric profile.

References Cited 8 UNITED STATES PATENTS 4/ 1942 Kenner. 12/ 1964Ellenrieder. 1/ 1966 Massoubre.

FOREIGN PATENTS 6/1964 Switzerland. 1/1961 France.

U.S. C1. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION leissue No. 26,713November 18, 1969 Henri Mirtain et al.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 2, lines 32 and 33, equation (1) should appear as shown below:

Column 5 line 22 "the first occurrence should read a Column 5 line 43"y-y" should read y-y Column 6 line 46, before "thereby" insert anitalicized comma; line 47, "lateral" should read lateral in italicsSigned and sealed this 8th day of December 1970.

SEAL) \ttest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

testing Officer

